The present invention relates to a coating composition, in particular a coating composition suited for use as a coating composition for automotive top coating.
Superhydrophobic fluororesin-containing coatings are known in the art as coatings excellent in stain resistance and suited for architectural, civil engineering or automotive use, among others. It has so far been considered that such superhydrophobic fluororesin-containing coatings hardly allow water to remain adhering to the surface thereof, hence stains can hardly be left on that surface.
In actuality, however, outdoor exposure of those coatings causes problems: the dirt in the atmosphere easily adheres to their surface and traces of rain water are readily left and deposited thereon. Therefore, for forming stain-resistant coating films with the surface thereof rendered hydrophilic, the international laid-open patent specification WO 94/06870 proposes a coating film forming method which comprises incorporating an organosilicate, such as methyl silicate or ethyl silicate, in a top coating and, after application of the resulting top coating, treating the coating film surface with an acid to thereby render the angle of contact with water not more than 70xc2x0.
However, even such coating compositions cannot provide sufficient stain resistance. When the silicate addition amount is increased for increasing the stain-resisting effect, the problems mentioned below may arise depending on the environmental conditions in the step of application. For example, under high humidity conditions, for example at a humidity of 80% or higher, in the step of setting or baking, appearance abnormalities, such as coating film cracks, may occur. Conversely, under low humidity conditions, for example at a humidity of 60% or below, the resulting coating films obtained may be turbid or show whitening after water resistance testing.
In view of the above-mentioned state of the art, it is an object of the present invention to provide a top coating composition which can provide coatings showing a good appearance irrespective of humidity conditions in the step of application and can provide them with good weathering resistance and stain resistance.
The present invention provides a top coating composition which comprises
a coating film-forming resin (I);
as well as a silicate compound (II) besides a hydrolyzable silyl-containing resin (III)
and/or a silicate-grafted resin (IV) resulting from graft polymerization of a silicate compound (II) onto a hydrolyzable silyl-containing resin (III).
The invention also provides a top coating composition as defined above
wherein said silicate compound (II) is a modified silicate compound represented by the general formula (1): 
xe2x80x83in the formula, n represents an integer of 1 to 30; at least one of the R1 groups is an organic group represented by R2xe2x80x94(Oxe2x80x94CH2xe2x80x94CHR3)mxe2x80x94, where R2 is an alkyl group containing 1 to 8 carbon atoms, a phenyl group or a benzyl group, R3 is a hydrogen atom or a methyl group and m is an integer of 1 to 4, and the remaining R1 groups each is a methyl or ethyl group.
The invention further provides a top coating composition as defined above
wherein said hydrolyzable silyl-containing resin (III) is an acrylic resin obtainable by radical polymerization of a silanol- and/or hydrolyzable silyl-containing, radical-polymerizable monomer (III-a), a hydroxyl-containing, radical-polymerizable monomer (III-b) and another radical-polymerizable monomer (III-c).
The invention still further provides a top coating composition as defined above
wherein said coating film-forming resin (I) comprises a hydroxyl-containing resin and a polyisocyanate compound.